1. Field of the Invention
The present invention relates generally to a cathode ray tube apparatus, and is directed more particularly to a cathode ray tube apparatus suitable for use with a high-brightness cathode ray tube used in, for example, a color projector.
2. Description of the Prior Art
In a prior art high-brightness cathode ray tube, the energy of an electron beam impinging on a phosphor screen is selected high to reproduce an optical image with high brightness. However, since the thermal conductivity of a front panel or glass panel, on which phosphor is coated, is low, upon especially continuous driving, it is difficult to diffuse or radiate heat and hence the temperature at the center of the panel is greatly increased. As a result, a so-called thermal quenching is caused in the phosphor. The thermal quenching is such a phenomenon that the brightness of the phosphor is lowered as the temperature is raised high. In this case, since the degree of the thermal quenching is different with the respective color phosphors, the white balance is disturbed. The disturbance of the white balance at the center of the phosphor screen results in that the picture quality is deteriorated remarkably. To avoid this, it may be considered that, in order to establish the white balance at the center of the panel, the brightness of other color phosphors is adjusted. This, however, results in that the white balance on the peripheral portion of the panel is disturbed and it becomes impossible to raise the brightness of the whole panel.
In order to avoid the increase in temperature on the front panel of the cathode ray tube which will cause the thermal quenching of the phosphor coated on the front panel, it is enough to provide a fan which will cool the surface of the panel. The fan, however, can introduce wind and dust to the panel surface to the panel surface. The dust then adheres to the panel surface to deteriorate the brightness thereof. The noise generated by the fan also proposes a problem.
To avoid the above defect, such an apparatus has been proposed, in which transparent cooling material or coolant such as convectable liquid is disposed in contact with the front surface of the panel to cool the front panel. The apparatus, however, is rather complicated in construction and is expensive.